1. Field of the Invention
The present invention relates to materials utilized in the construction of a game ball. The invention concerns, more particularly, a game ball that incorporates a polymer foam processed with an inert fluid blowing agent, such as nitrogen.
2. Description of Background Art
The game of soccer is played on a turf field having a length of approximately 100 meters and goals located at opposite ends of the field. Competing teams attempt to advance a soccerball, which is also referred to as a football, along the length of the field in opposite directions without using their hands to grasp or otherwise affect movement of the soccerball. The object of the game of soccer is for the players of one team to cooperatively advance the soccerball and place the soccerball into their designated goal, thereby scoring a point. Simultaneously, the other team attempts to cooperatively thwart the advance so as to regain possession of the soccerball and advance the soccerball toward the opposite goal.
The Fédération Internationale de Football Association (FIFA) promulgates standards that rank soccerballs as being either approved or inspected. Soccerballs bearing the approved denomination are generally recognized as embracing the quality necessary for international competition, whereas soccerballs bearing the inspected denomination may be utilized for lower competition levels or practice. In order to qualify for the approved denomination, a soccerball must fall within a narrow range of tolerances based upon such properties as weight, circumference, sphericity, pressure loss, water absorption, rebound, and shape and size retention.
The standards set by FIFA generally relate to the physical properties and performance of the soccerball rather than the specific structure of the soccerball or the materials utilized in the various components of the soccerball. Accordingly, soccerball manufacturers often vary the structure and materials of commercially-available soccerballs in an attempt to enhance the physical properties of the soccerball. In general, however, modern soccerballs have a substantially conventional configuration, as discussed below.
A conventional soccerball is substantially spherical and has a layered construction that includes a cover, a supportive structural lining, and an inflatable bladder. The cover is generally formed from a plurality of durable, wear-resistant panels that are stitched together along abutting sides to form a closed surface. The traditional soccer ball cover is modeled on a regular, truncated icosahedron and includes, therefore, twenty hexagonal panels and twelve pentagonal panels, and a plurality of other panel configurations are also conventionally utilized. Although the cover may be formed from full-grain leather, the cover of conventional soccerballs is often formed from polyurethane or polyvinyl chloride materials. The lining is generally located between the cover and the bladder to resist the outward pressure provided by the bladder, thereby retaining a spherical and dimensionally-consistent shape. Depending upon the manufacturer, the lining may be formed of natural cotton textiles, polyester textiles, or textiles that incorporate both cotton and polyester fibers. In addition to textiles, the lining may also incorporate a latex layer, for example. The bladder, which is the inner-most layer of the conventional soccerball, is formed of a material that is substantially impermeable to air, such as natural rubber, butyl rubber, and polyurethane. The bladder generally includes a valved opening, accessible through the cover, to facilitate the introduction of air. When inflated, the bladder expands and places a uniform outward pressure on the lining and cover, thereby inducing the soccerball to take a substantially spherical shape.
In addition to the cover, lining, and bladder, a soccerball may also incorporate a polymer foam layer to enhance pliability and cushioning. The foam layer generally has a thickness of 1 to 2 millimeters and is positioned between the cover and lining. Suitable materials for the foam layer include most polyolefin foams, which are prepared by the polymerization of olefins as the sole monomers. Examples of polyolefin foams include polyethylene, polypropylene, and ethylvinylacetate.
A first manufacturing process commonly employed to produce polyolefin foam suitable for the conventional soccerball utilizes chlorofluorocarbons, hydrofluorocarbons, or volatile hydrocarbons as a blowing agent. The resulting polyolefin foam is not cross-linked and may release chemicals that are considered to be detrimental to the global environment. A similar release of chemicals may also result from errors in the manufacturing process itself.
A second manufacturing process commonly employed to produce polyolefin foam suitable for the conventional soccerball utilizes a chemical blowing agent that expands through a decomposition reaction. In manufacturing the foam, a chemical such as azodicarbonamide is incorporated into polyolefin resin. A decomposition reaction involving the azodicarbonamide is then initiated by heat and produces gasses, such as nitrogen, carbon monoxide, carbon dioxide, and ammonia. The various gasses expand the polyolefin resin, thereby producing the polyolefin foam. A significant portion of the azodicarbonamide remains as residue, however, within the resulting polyolefin foam. Depending upon the density of the polyolefin foam, approximately 10% of the foam weight may be due to the azodicarbonamide residue. Accordingly, only 90% of the polyolefin foam weight is available to contribute to the mechanical performance of the polyolefin foam. Furthermore, if a soccerball incorporating a polyolefin foam is exposed to high ambient temperatures, then the azodicarbonamide decomposition reaction may reinitiate, thereby altering the properties of the polyolefin foam within the soccerball.